Research On Channel Selection Strategy In Cognitive Radio Network

The increasing demand for spectrum resources,the shortage of spectrum resources and the low effective utilization rate of spectrum resources all urgently require a new spectrum access strategy to solve.Cognitive users in cognitive radio(CR)can access idle channels opportunistically,thus improving the utilization rate of spectrum resources.In this paper,the channel selection strategy in the dynamic access process is deeply studied: by comparing and analyzing the characteristics of existing channel selection strategies,new channel selection strategies are studied.The specific content is as follows:Firstly,aiming at the problem of different idle probability and gain of each channel in cognitive radio network(CRN),in order to enable cognitive users to transmit successfully,the successful completion probability of cognitive users is introduced,and an optimal channel selection strategy based on maximizing system throughput is proposed.This strategy comprehensively considers channel gain,channel idle probability,and access channel probability of cognitive users to obtain the channel selection optimization model.Considering that the system throughput reflected by the objective function in this model only depends on the access channel probability of cognitive users,a genetic algorithm is designed to solve this optimization problem by controlling the probability.And the channel selection process is given.By comparing the access probabilities of all cognitive users on a certain channel,the cognitive user with the highest probability is selected to access the channel.Numerical simulation are conducted to analyze the performance of this strategy in terms of system throughput,transmission delay and communication outage probability.It is shown that this strategy has better throughput and can significantly reduce transmission delay and outage probability of cognitive users.Secondly,considering the situation that cognitive users fail to access the channel,a channel selection strategy based on the three-dimensional continuous time Markov chain(CTMC)model is proposed by adding a certain buffer space to the cognitive radio network model.In this strategy,the cognitive user with a transmission request selects the channel with a channel idle time greater than its transmission time,instead of the channel with the longest idle time.When the cognitive user fails to access the channel,the cognitive user is buffered to wait for the next opportunity to transmit,thereby avoiding the situation that some channels may be wasted during the period when the system becomes idle and the next cognitive user accesses.By considering the three indicators of the number of primary users and cognitive users in the system as well as the buffer capacity,the three-dimensional Markov chain of primary users and cognitive users are established by the arrival and departure of primary users and cognitive users respectively.And the three layers are distinguished by the number of buffered cognitive users.The established three-dimensional Markov chain accurately describes the primary user and cognitive user systems.In the establishment process,not only the state transition process of the primary users and the cognitive users when they arrive and departure is considered,but also the situation of whether all channels in the system are occupied and the number of cognitive users who fail to reach the channel are considered.By solving the steady-state equation of Markov chain rate,two performance indexes of spectrum opportunity utilization and successful transmission probability of cognitive users are obtained.The performance of this strategy in terms of spectrum opportunity utilization rate and successful transmission probability is analyzed through numerical simulation,which shows that this strategy can significantly improve spectrum opportunity utilization rate and successful transmission probability.